The mechanisms by which a single-celled embryo develops into a complex multi-cellular organism remain intriguing problems in biology. We have been using the nematode Caenorhabditis elegans as an experimental animal to investigate the components required for proper embryonic development of a particular tissue, the intestine. To identify genes whose products are required for proper specification of the intestinal lineage, we have isolated maternal effect lethal mutants whose defective embryos fail to develop intestinal tissue. These mutants fall into two classes; par mutants, presumed to have defects in partitioning of cytoplasmic components, and gut mutants, which have visible defects in the gut lineage. We intend to pursue this research by isolating additional mutants in these genes, particularly the gut genes, so that we have multiple alleles of each gene and have identified at least the majority of genes of this class. Mutants will be mapped genetically and their early lineages will be analyzed microscopically. They will be characterized with antibody probes to show that they fail to make antigens specific to intestinal cells but that they do produce an antigen specific to other differentiated cell types. Mutants will be obtained following mutagenesis with gamma-irradiation or by "transposon tagging" to obtain alleles that will be used to clone these genes. Selected genes will be cloned and sequenced, and their deduced amino acid sequence compared to that of known proteins in computer databanks. Antibodies will be prepared to gut gene polypeptides and will be used as probes to analyze the location of gut gene proteins in the developing embryo. Portions of the gene essential for proper regulation and protein function will be examined by in vitro mutagenesis and transformation into C elegans.